R. Corstanje

Assessment of the spatial distribution of soil properties in a northern everglades marsh

Florida Everglades restoration plans are aimed at maintaining and restoring characteristic landscape features such as soil, vegetation, and hydrologic patterns. This study presents the results from an exhaustive spatial sampling of key soil properties in Water Conservation Area 1 (WCA 1), which is part of the northern Everglades. Three soil strata were sampled: floc, upper 0- to 10-cm soil layer, and 10- to 20-cm soil layer. A variety of properties were measured including bulk density (BD), loss on ignition (LOI), total phosphorus (TP), total inorganic phosphorus (TIP), total nitrogen (TN), total carbon (TC), total iron (TFe), total magnesium (TMg), total aluminum (TAl), and total calcium (TCa). Interpolated maps and model prediction uncertainties of properties were generated using geostatistical methods. We found that the uncertainty associated with spatial predictions of floc, particularly floc BD, was highest, whereas spatial predictions of soil chemical properties such as soil Ca were more accurate. The resultant spatial patterns for these soil properties identified three predominant features in WCA 1: (i) a north to south gradient in soil properties associated with the predominant hydrological gradient, (ii) areas of considerable soil nutrient enrichment along the western canal of WCA 1, and (iii) areas of considerable Fe enrichment along the eastern canal. By using geostatistical techniques we were able to describe the spatial dynamics of soil variables and express these predictions with an acceptable level of uncertainty.

Adaptation of the CAS test system and synthetic sewage for biological nutrient removal: Part I: Development of a new synthetic sewage

A new synthetic medium has been developed for routine use in laboratory-scale sewage treatment simulation and biodegradation tests, such as OECD guideline 302A & 303A or ISO method 11733. The new medium, Syntho, was designed to meet the following objectives: 1) to be more representative of real sewage than the existing standard OECD synthetic sewage, 2) the COD:N:P ratio and mineral composition must allow a good degree of biological nutrient (N, P) removal, and 3) the medium should result in stable unit operation, including good sludge settling and minimal need for control actions. The IAWQ Activated Sludge Model No. 2 (ASM2,) was used to help design the medium and predict reactor performance for different possible media compositions. The results obtained with Syntho indicate that Continuous Activated Sludge (CAS) units with or without nutrient removal can be operated routinely on this feed. The new medium was also characterized by means of a respiration test. The different influent fractions applied in the model were validated, and a respiration profile indicated that Syntho is a close approximation of real sewage.

Carbon implications of converting cropland to bioenergy crops or forest for climate mitigation: a global assessment

The potential for climate change mitigation by bioenergy crops and terrestrial carbon sinks has been the object of intensive research in the past decade. There has been much debate about whether energy crops used to offset fossil fuel use, or carbon sequestration in forests, would provide the best climate mitigation benefit. Most current food cropland is unlikely to be used for bioenergy, but in many regions of the world, a proportion of cropland is being abandoned, particularly marginal croplands, and some of this land is now being used for bioenergy. In this study, we assess the consequences of land‐use change on cropland. We first identify areas where cropland is so productive that it may never be converted and assess the potential of the remaining cropland to mitigate climate change by identifying which alternative land use provides the best climate benefit: C4 grass bioenergy crops, coppiced woody energy crops or allowing forest regrowth to create a carbon sink. We do not present this as a scenario of land‐use change – we simply assess the best option in any given global location should a land‐use change occur. To do this, we use global biomass potential studies based on food crop productivity, forest inventory data and dynamic global vegetation models to provide, for the first time, a global comparison of the climate change implications of either deploying bioenergy crops or allowing forest regeneration on current crop land, over a period of 20 years starting in the nominal year of 2000 ad. Globally, the extent of cropland on which conversion to energy crops or forest would result in a net carbon loss, and therefore likely always to remain as cropland, was estimated to be about 420.1 Mha, or 35.6% of the total cropland in Africa, 40.3% in Asia and Russia Federation, 30.8% in Europe‐25, 48.4% in North America, 13.7% in South America and 58.5% in Oceania. Fast growing C4 grasses such as Miscanthus and switch‐grass cultivars are the bioenergy feedstock with the highest climate mitigation potential. Fast growing C4 grasses such as Miscanthus and switch‐grass cultivars provide the best climate mitigation option on ≈485 Mha of cropland worldwide with ~42% of this land characterized by a terrain slope equal or above 20%. If that land‐use change did occur, it would displace ≈58.1 Pg fossil fuel C equivalent (Ceq oil). Woody energy crops such as poplar, willow and Eucalyptus species would be the best option on only 2.4% (≈26.3 Mha) of current cropland, and if this land‐use change occurred, it would displace ≈0.9 Pg Ceq oil. Allowing cropland to revert to forest would be the best climate mitigation option on ≈17% of current cropland (≈184.5 Mha), and if this land‐use change occurred, it would sequester ≈5.8 Pg C in biomass in the 20‐year‐old forest and ≈2.7 Pg C in soil. This study is spatially explicit, so also serves to identify the regional differences in the efficacy of different climate mitigation options, informing policymakers developing regionally or nationally appropriate mitigation actions.

Defining and quantifying the resilience of responses to disturbance: a conceptual and modelling approach from soil science

There are several conceptual definitions of resilience pertaining to environmental systems and, even if resilience is clearly defined in a particular context, it is challenging to quantify. We identify four characteristics of the response of a system function to disturbance that relate to “resilience”: (1) degree of return of the function to a reference level; (2) time taken to reach a new quasi-stable state; (3) rate (i.e. gradient) at which the function reaches the new state; (4) cumulative magnitude of the function (i.e. area under the curve) before a new state is reached. We develop metrics to quantify these characteristics based on an analogy with a mechanical spring and damper system. Using the example of the response of a soil function (respiration) to disturbance, we demonstrate that these metrics effectively discriminate key features of the dynamic response. Although any one of these characteristics could define resilience, each may lead to different insights and conclusions. The salient properties of a resilient response must thus be identified for different contexts. Because the temporal resolution of data affects the accurate determination of these metrics, we recommend that at least twelve measurements are made over the temporal range for which the response is expected.

Landscape scale estimation of soil carbon stock using 3D modelling

Soil C is the largest pool of carbon in the terrestrial biosphere, and yet the processes of C accumulation, transformation and loss are poorly accounted for. This, in part, is due to the fact that soil C is not uniformly distributed through the soil depth profile and most current landscape level predictions of C do not adequately account the vertical distribution of soil C. In this study, we apply a method based on simple soil specific depth functions to map the soil C stock in three-dimensions at landscape scale. We used soil C and bulk density data from the Soil Survey for England and Wales to map an area in the West Midlands region of approximately 13,948 km(2). We applied a method which describes the variation through the soil profile and interpolates this across the landscape using well established soil drivers such as relief, land cover and geology. The results indicate that this mapping method can effectively reproduce the observed variation in the soil profiles samples. The mapping results were validated using cross validation and an independent validation. The cross-validation resulted in an R(2) of 36% for soil C and 44% for BULKD. These results are generally in line with previous validated studies. In addition, an independent validation was undertaken, comparing the predictions against the National Soil Inventory (NSI) dataset. The majority of the residuals of this validation are between ± 5% of soil C. This indicates high level of accuracy in replicating topsoil values. In addition, the results were compared to a previous study estimating the carbon stock of the UK. We discuss the implications of our results within the context of soil C loss factors such as erosion and the impact on regional C process models.

The Short-Term Effects of Prescribed Burning on Biomass Removal and the Release of Nitrogen and Phosphorus in a Treatment Wetland

Nutrient removal by constructed wetlands can decline over time due to the accumulation of organic matter. A prescribed burn is one of many management strategies used to remove detritus in macrophyte-dominated systems. We quantified the short-term effects on effluent water quality and the amount of aboveground detritus removed from a prescribed burn event. Surface water outflow concentrations were approximately three times higher for P and 1.5 times higher for total Kjeldhal nitrogen (TKN) following the burn event when compared to the control. The length of time over which the fire effect was significant (P < 0.05), 3 d for TKN and up to 23 d for P fractions. Over time, the concentration of soluble reactive phosphorus (SRP) in the effluent decreased, but was compensated with increases in dissolved organic phosphorus (DOP) and particulate phosphorus (PP), such that net total P remained the same. Total aboveground biomass decreased by 68.5% as a result of the burn, however, much of the live vegetation was converted to standing dead material. These results demonstrate that a prescribed burn can significantly decrease the amount of senescent organic matter in a constructed wetland. However, short-term nutrient releases following the burn could increase effluent nutrient concentrations. Therefore, management strategies should include hydraulically isolating the burned area immediately following the burn event to prevent nutrient export.

Site-specific land management of cereal crops based on management zone delineation by proximal soil sensing

Management zone (MZ) delineation can be improved by acquiring high-resolution data on soil and crop properties. This hypothesis was tested by directly comparing three fertiliser application schemas – each derived from different MZ delineation approaches. A uniform-rate (UR) scheme was used alongside two variable-rate methods. One replicated the traditional mapping of fertility-based MZ (VR1), the other employed soil property maps derived from a visible near-infrared (vis-NIR) on-line sensor (VR2). Results showed that VR2 produced higher yields of oil-seed rape (OSR) per hectare than both the traditional and uniform application in the same study field for the 2012 crop. This method also used slightly less nitrogen (N) fertiliser than the UR, indicating that it has both economic and environmental benefits.

Two Methods for Using Legacy Data in Digital Soil Mapping

Legacy data are useful sources of information on the spatial variation of soil properties. There are, however, problems using legacy data, and in this paper we explore some of these problems. A common issue is often the uneven sample distribution over geographical and predictor space and the problems this generates for the subsequent modelling efforts. Furthermore legacy soil data often has a mixture qualitative and quantitative data. The current need is for quantitative data, whereas the available datasets are often qualitative; e.g. auger bores. In this paper we compare two methods:(i) a Generalized Linear modelling (GZLM) approach which uses scarce,measured soil property data and (ii) Bayesian Belief networks (BBN) which uses extensive but generic values of the soil property, linked to soil classes. We used digital soil mapping covariates such as small scale soil maps, geology, digital terrain model, climate data and landscape position in order to predict continuous surfaces for sand, silt, clay, bulk density and organic carbon. The objective is to present a qualitative comparison between the two methods, as a direct comparison was not possible due to the number and distribution of the legacy data. We found that the GZLM approach was significantly impacted by an uneven sampling of the predictor space. This study suggests that a more generalist approach such as BBN is better in the absence of few hard data but in the presence of many soft data.

Linkages Between Microbial Community Composition and Biogeochemical Processes Across Scales

Much of the biogeochemical cycling that is critical to the functioning of wetlands is controlled by complex communities of microorganisms (Fig. 11.1). These communities form the basis of detrital food webs which mineralize nutrients bound up in plant biomass and are therefore a critical link in the nutrient cycles that drive wetland ecosystems. Considerable research has been conducted in recent years to define energetic controls on biogeochemical cycles in wetlands, and a basic knowledge of the ecology and physiology of individual groups of many of the microorganisms responsible for biogeochemical cycling has existed for many years. Much previous research regarded wetland microbial communities as merely biomass, however, with little regard for the activities or numbers of individual groups that control these functions. Individual components of these communities respond differently to changes in their environment, which in turn may affect the rates and pathways for biogeochemical cycles in wetlands. Anthropogenic impacts resulting from air and nutrient pollution and increased atmospheric CO2 concentrations effect biogeochemical processes in wetlands, but the mechanisms by which these changes occur cannot be fully understood until the ecology of the key microorganisms in these systems is understood. Linking microbial community structure and activities with biogeochemical cycles will provide greater insight into the mechanisms that drive these cycles and how they respond to anthropogenic impacts. The development and application of new tools and new approaches to the characterization of microbial communities and their activities leads to increased appreciation of the roles of individual functional groups of bacteria

Soil microbial ecophysiology of a wetland recovering from phosphorus eutrophication

Soil phosphorus (P) enrichment from external inputs can result in considerable changes in wetland ecosystem structure. What is not known is whether many of the microbial physiological measures that are effective at determining ongoing impact are equally sensitive to reductions in the soil P content. The study was conducted over a two year period (1999–2000) in two areas located in Blue Cypress Marsh Conservation Area (BCMCA), an area (Enriched) with historically elevated soil P (1,544 mg kg−1 in 1995, 877 mg kg−1 in this study) and a reference area (Reference) with background soil P contents (698 mg kg−1). Nutrient loading to this wetland was terminated in 1994. Microbial ecophysiology measures were obtained quarterly and consisted of soil microbial biomass carbon (MBC) content, β-glucosidase and acid phosphatase, and end products of anaerobic microbial metabolism (CO2 and CH4). All measures exhibited significant temporal variation with higher values for MBC content, enzyme activities, and respiration rates during summer months (June and September) and lower in the winter months (December and March). We found no significant differences between site mean MBC (Enriched: 7.24, Reference: 8.22 mg−1 kg−1), CH4 production (Enriched: 4.41, Reference: 4.73 μmol CH4 gr−1 d−1), or β-glucosidase activity (Enriched: 56.14, Reference: 57.70 μg MUF gr−1 h−1). The site mean acid phosphatase (Enriched: 56.92, Reference: 78.74 μg MUF gr−1 h−1) and CO2 production rates (Enriched: 11.00, Reference: 13.69 μmol CO2 gr−1 d−1) were found to be significantly different. Microbial communities at the two sites were different in terms of their metabolic activities, but not in terms of C-pathways. We also found that enzyme profiles at the enriched site did not change appreciably over the two year period. The results obtained in this two year study suggest that most microbial community ecophysiology measures were not responsive to decreasing concentrations of P. However, at both sites, β-glucosidase and anaerobic microbial activities were higher in the second year (41.80 vs. 68.27 μg MUF gr−1 h−1 and 10.34 vs.13.85 μmol CO2 gr−1 d−1) and acid phosphatase activities lower (72.54 vs. 63.11 μg MUF gr−1 h−1). A drawdown that took place in the winter months of late 1999 and early 2000 might have released labile soil components, resulting in increases in overall metabolic activities and repression of the acid phosphatase activities. This has management consequences as P from the enriched areas can be remobilized and move further downstream in surface water.